A gas insulated switchgear (hereinafter referred to as “GIS”) has such a construction that, in coupling a plurality of cylindrical containers in which high-voltage electric conductors or various high-voltage apparatuses are accommodated, sealed compartments are formed using disk-shaped insulating spacers formed from insulating material such as epoxy resin and each of the sealed compartments of the cylindrical container is filled with insulating gas.
For the measuring of current flowing through the electric conductors in the cylindrical container, a GIS uses a wound-type current transformer or an optical current transformer that uses an optical fiber having Faraday-effect. Since small sizing and weight reducing is a requirement of a GIS, use of the current transformer particularly considers employing an optical current transformer, which offers size reduction to a larger degree compared with a wound-type current transformer. As a current transformer for GIS use, an optical current transformer that Japanese Patent Laid-open Application No. Hei 10-142265 (Patent literature 1) describes is known.
The optical current transformer described in Patent literature 1 is installed in a manner as follows: In coupling a plurality of cylindrical tanks having flanges for connection, a three-phase insulating spacer of insulating material that has electric conductors for three phases is disposed between the flanges in a sandwiched manner. In this three-phase insulating spacer, optical fibers of Faraday-effect element to form optical paths for light transmission and light reception are embedded severally surrounding each of the three-phase electric conductors.
On the optical fiber for light transmission, a setup of devices for the light transmission side, comprised of a light source, a polarizer, and other related elements, is arranged outside the tank; and likewise on the optical fiber for light reception, a setup of devices for the light reception side (detector side), comprised of an analyzer, a measuring instrument, and other related elements, is arranged outside the tank. Thereby, an optical current transformer is formed. In the optical current transformer, a linearly polarized light is injected into the optical path from the light emission side for transmission, and at the detector side, the transmitted light is detected and measured for its Faraday rotation angle, magnitude of which is dependent on the intensity of action of magnetic field generated by current flowing through the electric conductor, and thereby the magnitude of the current in the electric conductor is determined.
On the other hand, a zero-phase current transformer for gas insulated electrical apparatuses has been disclosed in Japanese Laid-open Patent Application No. Hei 8-178987 (Patent literature 2). The configuration of this zero-phase current transformer is as follows: An optical fiber of Faraday-effect element is embedded in a three-phase insulating spacer having electric conductors for three-phase, encircling all the electric conductors of three-phase in one lump over the zero-phase current detection section of such electric conductors. On each end of the optical fiber, a setup of devices for the light transmission side and a setup of devices for the light reception side are severally arranged. Thereby, the zero-phase current is determined based on the polarization signal outputted through the optical fiber.
The optical current transformer described in Patent literature 1 stated above uses such an insulating spacer that optical fibers are embedded therein severally surrounding the electric conductor of each phase; and the zero-phase current transformer described in Patent literature 2 uses an insulating spacer that an optical fiber is embedded therein surrounding all the electric conductors of three-phase in one lump. These insulating spacers are manufactured using, in general, insulating material such as epoxy resin.
Usually, an insulating spacer of insulating material may sometimes involve a tiny gap, which is commonly referred to as a void, during molding process of embedding electric conductors. This tiny gap causes corona discharge because of electric field formed by electric conductor energizing and possibly brings about electrically adverse effect. Further, there is a problem. Securing the insulating spacer on the flange of the cylindrical tank needs use of a plurality of through bolts; the through bolts disturb the uniformity of electric field around the outer periphery of the insulating spacer. To avoid this kind of harmful influence, a configuration has been employed in which a grounding shield that surrounds electric conductors as a whole is molded in the insulated spacer in one lump, and thereby, the electrical adverse effect attributable to tiny voids is prevented by the grounding shield.
It may be practicable to add a grounding shield in manufacturing the insulating spacer of Patent literatures 1 and 2. However, the simultaneous molding of electric conductors together with an optical fiber and further with a grounding shield integrally into one body does not sufficiently eliminate the electrical adverse effect attributable to tiny voids; this is a problem against an eased manufacturing.
An object of the present invention is to provide an insulating spacer with built-in optical fiber, which includes an optical fiber for current transformer use, having features such that manufacturing is easy and economical, such that corona discharges attributable to electric field concentration in tiny gaps will not be generated, and such that the properties of the current transformer will not be affected.